Studies are in progress to investigate the stereospecific biliary secrection of an organic anion, iopanoic acid. Initial studies in vivo have demonstrated that (+)-iopanoic acid is secreted into bile to a significantly greater extent than (-)-iopanoic acid. The hepatic content of the acylglucuronide of each enantiomer, expressed as a function of the hepatic content of the parent compound, suggests that the observed difference is not attributable to differences in metabolism alone. Since it has already been demonstrated that the kinetics of iopanoic acid in the isolated rat hepatocyte is similar to that observed in the intact rat, the kinetics of the enantiomers of iopanoic acid will be studied in the hepatocyte preparation. Studies will be performed on the uptake, metabolism, and secretion of iopanoate to determine the basis of the altered secretion of the enantiomers. Further studies will be performed to determine the site of the inhibition for biliary secretion that is known to occur between various organic anions.